wirelessguy

I am starting a thread on GPZ discrimination.  In this missive I use “discrimination” with reference to both hot rock and junk identification. 

Let me start with my hypothesis then describe how I got there.   I am very much asking for corroborating or contradictory evidence to my hypothesis and other notes as well as any other useful info on GPZ 7000 discrimination.

Hypothesis:

Natural gold from small, barely perceptible signal return, to huge enough to provide overload, always produces a high-to-low tone when in high yield gold mode / general ground type settings.  Natural Gold can sound either high-to-low or low-to-high in difficult or severe ground type settings.  Ground type is the only user changeable setting that effects tone changes high-to-low or low-to-high on a particular target.

Required Conditions:  negligible EMI, negligible other metal or overriding hot rock present.

The one thing that has been true to date in my field experience and experiments, is that every natural gold find or test nugget from small, barely perceptible to huge enough to provide overload, had a high-to-low tone when in high yield/general.  I understand this hypothesis is no giant breakthrough enabling classification of the Zed as anything other than an all-metal machine as the Minelab manual and advertising clearly classify it.  Nonetheless, it’s the entire useful conclusion I’ve come to in as few words I can make it.  (I have trouble with writing few words.  J  )   Minelab makes no mention of discriminating sounds yet the pitch change of high-to-low or low-to-high is impossible to ignore, and naturally causes the curious to explore.* 

Early in my experimentation and Zed education, I spent hours determining what controls affected a reliable pitch change in different junk materials and hot rocks and gold.  All kinds of elaborate charts in my notebook.  I am glad I have not posted on this topic earlier because I have been through many cycles where experiments and field experiences would give me some preliminary beliefs which would soon thereafter be disproved by another experiment or field experience.

What has emboldened me to make this post (as simple as the hypothesis is) is that I was fortunate recently to experiment on a very large gold in quartz specimen.  Not certain on the mass of gold (> several ozs for sure) yet the return signal easily produces overload response on all gold type/ground type combinations. (No, not my gold.  L )   The specimen produced high-to-low on high yield/general, low-to-high for difficult and severe ground types.  Always true as I backed the Zed coil away from the specimen.

This was enlightening and counter to my early Zed experimentation on aluminum where size of aluminum changed pitch direction.  I found that the Zed, with no change in settings, will respond high-to-low on small pieces of aluminum foil (several mm x several mm) yet respond low-to-high on large (>100 mm x >100 mm) keeping high yield/general constant as well as all other settings.   Zed responds low-to-high on soda and beer cans with high yield/general.    So, I have wandered about assuming the same for gold (size of metal can affect pitch change) and hence I have NO DISCRIMINATION at all.   I “convinced” myself of this when I tested a 1 gram nugget (high-to-low) then a very large men’s gold wedding band (low-to-high) keeping high yield/general constant as well as all other settings.   Hence my hypothesis states “natural gold” to distinguish from alloys.

Hot rocks, iron or mineral based, produce a symphonic range of return sounds and can be high-to-low or low-to-high on any ground type or gold mode setting.   (another thread necessary on hot rock strategies.)  My hypothesis of “Ground type is the only user changeable setting that effects tone changes high-to-low or low-to-high on a particular target.” is not in conflict with the fact that you can put audio smoothing on high and totally eliminate a return from a weak target.   Audio smoothing setting does not change the pitch direction on a target.

Iron.  Man made iron and high % iron alloy objects produce low-to-high on all ground types only if the iron is not rusted heavily.  If the iron is rusted it can produce high-to-low or low-to-high.   This of course is near useless info for the prospector because most all iron stuff we find is rusted. 

Since I work in a hard rock environment, "dig it all" is just not practical.   Hence, my experiments and documentation on the GPZ7000 tones to try and get any possible discrimination info out of it. In my environment, that mostly means hot rock.  In my environment, I can prospect in high yield/general at least 90% of the time.  Mineralization puts me in difficult or severe less than 10% of the time.  I also have the “luxury” to mark interesting signal location first located by GPZ, then come back with my Whites MXT to try and discriminate.  (Also have GMT, GB II and GB Pro available.)  This works well on strong signals, or near-surface hot rock, however weaker GPZ signals produce inadequate response for any accurate discrimination from the VLFs.

Even if your environment requires you to mostly search in difficult or severe ground type settings, you could always go high yield/general as a discrimination test right over the target.  Of course then you might have "overriding hot rock" condition.   I think the most opportunity for uselessness of my hypothesis, even if it's accurate, is that I just don't have much experience of gold in difficult or sever ground environments whereas that is much the norm elsewhere.

* My previous Minelab experience is just ~ 80 hours with a GP3000, so I come to GPZ 7000 without much Minelab audio discrimination experience.  I’m told on other posts in this forum that is a Zed education advantage.

tvanho, if you are comfortable with your iPhone or Android phone I agree with Norvic that you already have a gps and camera and compass.  Get a purpose built rugged case if it's something you'll take in the bush.  I use google maps on both android and iphone and it's adequate for basics and is simpler than a dedicated gps for sure.  Very few menus to figure out and if you use google maps on a computer easier yet.

I use my phone gps for off and on road vehicular travel, cause I always have my phone then.  When I'm in the bush I use a dedicated gps 'cause I'm a gadget guy,  my dedicated gps has better location performance (be sure to get a dual mode glasnoss/gps), I like and use a lot of the features, it's inherently much much more rigged.

As far as a camera helping you with general gps usage, I dunno.  Never thought of it 'til I read your post.

I agree this is the best informative place to get good reliable information from a bunch of very knowledgeable bunch of individuals. Kinda like one stop shopping,without the salesman. Rick.

My sentiments exactly

Super informative and clarifying video and thread!   Helps me a ton.  Thanks Steve, JP and other contributors.   My own experience and tests in my environment (all in a hard quartz - mild ground - environment) also do not show benefits or uses for general and extra deep.   High Yield gives me a more definiitive response all my tests to date over general and extra deep.  And now I know why insofar as extra deep is concerned - I haven't tested in heavily mineralized ground.     Still learning!

Maybe I will find a useful strategy using these two gold modes for discerning different types of problematic hot rock I do encounter ???

A question:  In this video for the detectorist, when Phil uses the phrase "push the detector hard" does he mean "increase the transmit coil current (power)" if he were speaking in electrical engineering terms?    

<SNIP> So then I went over the same ground again, but this time I shifted the Zed into hyperdrive by switching to the High Yield gold mode, and suddenly that elusive gold that I knew was there lit up like the Fourth of July! <SNIP>

Lunk Thanks for this good thread documenting your early results with the Zed.  Informative and inspirational!  The quote above, along with this super informative thread http://www.detectorprospector.com/forum/topic/826-minelab-video-gpz-7000-gold-mode/ give more evidence that High Yield is the go to Gold Mode in most instances.    I have found that to be true in my first few weeks experience with the Zed hunting in hard quartz which regionally or occasionally contains various hot rock.    I have yet to find a proven benefit for the general or extra deep gold modes in my application; and to be clear, I am still learning.

Gold Hound

Posted Yesterday, 12:03 AM

Reno Chris, on 20 Mar 2015 - 11:02 PM, said:

Radiant energy disperses into all three dimensions and so decreases in the cube of the distance. So it's the inverse distance cubed.

since the.energy goes out both from the coil and then from the target back to the receive coil, the total energy loss in both directions is the distance times 10 to the 6th power, or a million times.

Look up 'inverse square law' on Wikipedia and you will se what I am talking about.

You're right about energy traveling out from the source in 3 dimensions, it travels out in an ever expanding sphere.

My explanation and mathematics are correct the inverse square law takes into consideration all 3 dimensions.

 

Gold Hound,

The total energy across a unit area of an electromagentic field in the far field decreases proportional to 1/r^2 with r being the distance from the radiator.   Far field by all definitions and approximations = more than a wavelength.  If we approximate the frequency involved with metal detection as 20 kHz we get 15,000 meters wavelength using c=(freq)(wavelegth)  with c= speed of light = 3*10^8 m/s.   So that is a range left for charlatans and heretics with their divining rods and long range locators.   So 1/r^2 is valid for distances far far greater than we are talking about finding gold nuggets.

And this paragraph above has nothing to do with metal detection using induction balance, pulse induction or zero voltage transmission.   That is because all metal detectors are based on induction principles - magnetic field only.  NOT electromagnetic plane waves (radio waves) propagation.  The metal detector coil is not an "antenna".

In my 30+ yrs of radio frequency engineering practice I find the concept of near field and far field as a function of wavelength used widely in electromagnetic plane wave (radio wave) practice and are not so much used in inductive (magnetic) field practice such as in the design and winding of inductors, transformers.  Specific geometries come far more into play governing the magnetic field strength at points in the area of interest.   

I blame all of the detector manufacturers for spreading over simplifed information on this subject when it is not that complcated.

 

I am still a relative newbie to metal detecting however have devoured literature (including tons of lore on blogs) on the details of the transmitted magnetic field from an MD coil and the return eddy current from the target to the receive coil.   I guess I differ with your statement above.  I find it extremely complicated.  I find the best simplification that exists on field strength that has merit in the physics of magnetic fields is the 1/r^3 approximation Reno Chris and jasong note.   ( I don't find Chris' reasoning above for the 1/r^3 approximation accurate).   I have read a few different credible reasonings for the field strength approximation of 1/r^3 under many applicable scenarios of dipole approximation of a current loop and size of area this applies to (size of target) relative to the loop.  1/r^3 approximation is widely quoted by strong technical people in the metal detector field.

As Chris notes, returned field strength loss vs distance becomes 1/r^6 if you consider transmit magnetic field to energize the target and the the return path of eddy current from target to the receive coil.   

HOWEVER, 1/r^3 is an approximation with multiple ifs and thens and the actual math is complicated particularly close to the coil.   I think the metal detector manufacturers must simplify all this physics with best visual models of cones and blades when it comes to using the metal detector.  Humans don't generally visualize in terms of graphs and equations.   So, the way that I, an inexperienced user, experienced RF engineer, reconcile statements that Steve H and others make about those cone and blade approximations is that these experienced users are integrating a lot of experience on different size targets at different distances, with different coils, in different conditions and using a lot attention to detail in their practice and have observed the physics exceptions to the visual approximation.  Good info, more nuanced than a brand_new_first_times_in_the_field metal detector user needs.

http://www.geotech1.com is a great site for the engineering and physics side of metal detecting if you have not already found it.    

I bought one of those half batteries (actually a refurbished battery) from the ebay guy at the link above.   You can send him your existing battery and he'll refurbish.  He also had some in inventory for sale when I bought a month ago.  Advertised at about 6 hrs run time. 

I recently bought a refurbished Minelab lead acid battery for GP series from this 100% positive feedback member on Ebay.

http://www.ebay.com/usr/miner_mark?_trksid=p2047675.l2559

Battery works great, price was right and delivery very prompt.  

"loose lips sink ships"   ...  indeed! 

What gets overlooked is that the GPZ is doing what the GPX can do with a bigger coil, or a smaller coil, or different timings, all at once with one setting and one coil. Yeah, I think the GPX in multiple passes with multiple coils and different settings can give a GPZ with a single setting and coil a run for the money in many cases. As long as you have time to hit the same ground multiple times. And even then, the GPZ will hit some gold a GPX just can't hit.

Any light bulbs?

 

BINGO!   I was thinking the exact same thing last night when I read this thread and the chart comparing GPZ and GPX 5000 having "same " performance and planned to pose in form of a Q this AM.  Steve insightfully answered my Q before I could write it!    As has been the case all over this excellent web site.

I am told by my USA dealer he should be able to ship my paid for GPZ 7000 early next week.  Can't wait! 

On 2/24/2015 at 9:06 AM, Steve Herschbach said:

<snip>

The entire Electronic Gold Rush has taken place in my adult lifetime and I am likely to see the day when there are only a few diehards left at it. The good news is in my opinion we are on the eve of what may possibly be the last gasp, the last breath of fresh air.

<snip>

 I have a chance to participate in what may very well be the last chapter of the electronic gold rush - The GPZ Gold Rush. 

<snip>

image.jpg

"640k is more memory than anyone will ever need"  

"everything that can be invented, has been invented"

I dunno Steve.   I don't think it's a good bet to bet against technological advances.    Electronic prospecting suffers from being such a small market worldwide.   There really are a very small number of talented engineers and scientists working on the problem. In a recent forum conversation with Carl Moreland on the topic he replied to me there are probably more engineers developing 35 mm film cameras than metal detectors today.   As you have noted Minelab seems to have no company biting its heels in second place.

I don't have a logical prediction of what will trump GPZ 7000 (assuming it proves to be another quantum success).

I'll throw a couple thoughts out though.   In most of my lifetime (and I'm the same age as you) technology advancements have mostly been made in corporations and by people working full time in the craft.   The only notable area where amateur hobbyists were consistent dabblers and improvers was ham radio.

In the last decade or so we've seen a huge rise in what's often termed the "maker movement".   It is a large groundswell of DIYers.  Not just technology for sure, even bloggers might loosely be in the movement.   In the last 10 years, a <$100 kit of microcontroller board with various I/O (input/output) and a simple programming language you can learn on your own and an internet of people teaching and sharing has become widespread. Readily available $10ish chips have more computing power than Apollo 11.    Doing this stuff is very quickly getting to more people who are interested and have chutzpah.

Maybe it's not low frequency induction based technology after the GPZ?   Imaging is advancing so rapidly.  In the 90s 1 MPixel was high def and expensive.   Add  image recognition which is growing in capability radically to cheap digital imagery and maybe someone can move ground penetrating radar (way more depth than induction techniques) into enough resolution to economically determine a nugget from a nail?   (I know, I know I know, ... a lot more issues than just that.  some engineers read this stuff  :-)  )

I am not predicting "what" specifically as much as I bet on "will" happen.  For sure some ebbs and floods just like the last two centuries of gold rushes.

Thanks for the link Steve.

Jasong, can you provide the patent number you are referring to please?  Any other GPZ 7000 relevant patents numbers appreciated as well.  thx

My professional wireless background is far more involved in audio headsets than metal detectors so I'll strive to be brief and specific on the  topics in this thread.  (brief is difficult for me)

On February 13, 2015 at 2:28 AM, vanursepaul said:

They dont use Bluetooth ---instead they use KLEER tech....(not very popular)

But i think they will work better than BT

Bluetooth (a technology brand) is indeed a more widely popular standard than Kleer (a company name which uses a proprietary technology).  Kleer based products almost always come in a pair a dongle (plugs into audio jack or maybe USB) and a headset.  Kleer main claims to fame are low latency and lossless audio (in laymen's terms this means very clear audio).   So, to support vanerspaul's assertion, you are not likely to go wrong with Kleer based audio jack dongle and headset.

Bluetooth headsets tend to be sold standalone to work with a phone, computer, tablet, which has an embedded bluetooth capability.    If you find a Bluetooth audio jack dongle and headset combination, look for "low latency A2DP".   Otherwise you may end up with a latency problem as Steve notes above.    

(OK, one nerdy thing -  for lip synch audio, matching video human speaking to audio, the rule of thumb is less than ~ 40mSec latency.   So in our application, matching MD swing (eyeball) to sound, look for less than 40 mSec latency on the specs of your headset audio dongle combo.)

To summarize for those not wanting to be wireless audio pros, you are less likely to make a mistake with Kleer based audio dongle and headset products.

The GPZ 7000 is based on a 2.4 GHz proprietary technology of Texas Instruments (per FCC submissions).   Bluetooth and Kleer also use the 2.4 GHz band.  2.4 GHz is not in and of itself magic.   There is crap and great audio stuff using the 2.4 GHz frequency band.   Minelab's choice of the TI technology means they are going to keep their wireless audio link a closed system so you can't go buy a wireless headset to mate with your GPZ 7000 directly.   You'll buy a corded audio headset to plug into the GPZ 7000 WM 12 just like on the CTX 3030 WM10 module.

Junkman, I'll speculate the Aussie marketeers ran into some Apple folk at a bar or conference and got a few pointers on "Hype 101".    We'll all forget about this phase of product introduction if the GPZ 7000 proves to be worthy like the first iPod, iPhone, iPad which indeed fully delivered.  

$9999.00 USD

Steve, in your GPZ 7000 specs page you note the standard search coil is a 14 inch double D.   Why do you believe double D?  Advert only says 14 inch.   Do you know if a mono will be available at launch, too?

Quadcopter drones are non-trivial to pilot.   Master flying one of the Hubsan X4 Quadcopters ($43 at Amazon) before you crash and burn a quad that can carry a camera.  Get the blade protector for $3.  

Thanks for the guess Steve.

I worked 7 yrs in a consumer/B2B market estimated at $2B worldwide.    There was one noteworthy market research firm covering that market which was dominated by 2 companies worldwide for the last 25 years.  That $2B market was not big enough to get Apple/Panasonic/Samsung/ ... interest nor get serious, well funded new player.  So, it stays a duopoly today and also lacks innovation.

Innovation is hard to do profitably.    The general public only sees the successes (Steve's XP example above) not the failures and wasted $.     Failures inside big well known companies and the myriads of failed start-ups.   This makes financially tightly managed companies tentative on innovative new product development and market introduction.    

Having said that, as a newbie detectorist, and > 30 year wireless engineer, executive, entrepreneur, (now well armed after reading Inside the Metal Detector !!!) I agree with Steve there is low hanging fruit for innovation in the MD industry.   

In addition to Steve's list I gotta believe there is much to be gained in digital signal processing in MDs for better discrimination -  the much desired "discrimination in a PI at depth" does not seem to me to be as much a pure physics problem as an application of minds and $ problem.

Thanks for the input, Mike.   Do you have any pointers on where to find figure 8 coil building tips other than the geotech site?  

What is the total $ size of the word-wide hobby metal detector market?    I dunno.   I'll guess that it is so small that no market research firm even studies it, hence we may not get any objective answer to my Q.

The biggest reason that there are few market releases of breakthru products, is that the market is so small there is relatively little money put into it.   

If there was a big growing market, consumer product companies with big $ would put more serious R&D into it.

Congrats Steve!  Beautiful specimen for sure.  

I have an application for a specialized metal detector coil. I want to use a Whites MXT to provide ferrous/non-ferrous discrimination information on targets which are deeper in quartz than common metal detector depths (2-30 feet). These targets were not found with found a metal detector.

I want to insert a metal detector probe encased in PVC pipe into a 2” dia hole bored into the quartz.

Reading Carl Moreland's “Coil Basics” tutorial at http://www.geotech1.com/cgi-bin/pages/common/index.pl?page=metdet&file=info.dat it seems to me one of the figure 8 configurations would work well in this application. I would insert the probe on adequate length sections of PVC into the drilled hole and connect to the MXT.

I’m armed with no metal detector probe building experience, a lot of RF experience, adequate test equipment.

Will this idea work in general?

Is one of the figure 8 configs the right topology?

Any other hints on making this probe before I start?

What distance from centerline of 2” dia drilled hole can I expect to discriminate on a US nickel sized object for ferrous/non-ferrous?

"Where would you have so much quartz that it would cover the ground?"

under the ground

Steve, thanks for the advice.   Makes sense.   More to advance my knowledge than to influence my backyard, can you comment on Q1 and Q2?